Subject: [PATCH 6/7] ARM: KVM: switch to a dual-step HYP init code

From: [email-masked] (Will Deacon)
Date: Wed, 3 Apr 2013 11:07:51 +0100

On Tue, Apr 02, 2013 at 02:25:14PM +0100, Marc Zyngier wrote:
> Our HYP init code suffers from two major design issues:
> - it cannot support CPU hotplug, as we tear down the idmap very early
> - it cannot perform a TLB invalidation when switching from init to
>   runtime mappings, as pages are manipulated from PL1 exclusively

[...]

> diff --git a/arch/arm/kvm/init.S b/arch/arm/kvm/init.S
> index 35a463f..b2c6967 100644
> --- a/arch/arm/kvm/init.S
> +++ b/arch/arm/kvm/init.S
> @@ -21,6 +21,7 @@
>  #include <asm/asm-offsets.h>
>  #include <asm/kvm_asm.h>
>  #include <asm/kvm_arm.h>
> +#include <asm/kvm_mmu.h>
>  
>  /********************************************************************
>   * Hypervisor initialization
> @@ -47,6 +48,9 @@ __kvm_hyp_init:
>  	W(b)	.
>  
>  __do_hyp_init:
> +	cmp	r2, #0			@ We have a SP?
> +	bne	phase2			@ Yes, second stage init
> +
>  	@ Set the HTTBR to point to the hypervisor PGD pointer passed
>  	mcrr	p15, 4, r0, r1, c2
>  
> @@ -96,14 +100,35 @@ __do_hyp_init:
>  	orr	r0, r0, r1
>  	isb
>  	mcr	p15, 4, r0, c1, c0, 0	@ HSCR
> -	isb
>  
> -	@ Set stack pointer and return to the kernel
> +	eret
> +
> +phase2:
> +	@ Set stack pointer
>  	mov	sp, r2
>  
>  	@ Set HVBAR to point to the HYP vectors
>  	mcr	p15, 4, r3, c12, c0, 0	@ HVBAR
>  
> +	@ Jump to the trampoline page
> +	ldr	r2, =#PAGE_MASK

Shifting right by PAGE_SHIFT can avoid the load.

> +	adr	r3, target
> +	bic	r3, r3, r2
> +	ldr	r2, =#TRAMPOLINE_VA
> +	add	r3, r3, r2
> +	mov	pc, r3
> +
> +	nop

<insert dead chicken and voodoo chant here>

> +
> +target:	@ We're now in the trampoline code, switch page tables
> +	mcrr	p15, 4, r0, r1, c2
> +	isb
> +
> +	@ Invalidate the old TLBs
> +	mcr	p15, 4, r0, c8, c7, 0	@ TLBIALLH
> +	dsb
> +	isb

You don't actually need this isb (there's an eret next!).

>  	eret
>  	.ltorg

Will